MAlCO3 Based Layered Double Hydroxides for Catalytic Depolymerization of Poly(ethylene terephthalate) and Poly(bisphenol A carbonate) Waste Materials

Abstract

Abstract Polyesters are most frequently used engineering polymeric materials however, polyethylene terephthalate (PET) and polycarbonate (PC) are vastly used polymers and considered as the valuable polymers for the production of fibres, containers, building materials, eyeglass lenses, CDs, DVDs, computer appliances, sports safety equipment. Because of their good tensile strength, thermal stability, chemical resistance and processability, which lead to continuous growth in their demand for widespread applications. The environmental accumulation, high resilience, and fast disposal with degradation/reusability/recycling of these plastics, have given rise to a global concern. The research has been laid in the development of methods for the recycling of these materials are important from environmental protection and resource sustainability point of view. In the present study, the catalytic depolymerization of PET and PC waste accomplished using MAlCO3 based layered double hydroxides (LDHs) and ethylene glycol (EG) into bis(2-hydroxyethyl terephthalate) (BHET) and bisphenol A (BPA) as the main products, respectively. The different type of LDHs combinations synthesized by substitution of different divalent metal ions (MAl-CO3 LDHs where M= Ni/Zn/Mg/Ca/ Co/Cu/Li/Pb/Cd/Mn) through co-precipitation method and characterized by using XRD, FTIR and SEM-EDX techniques. The reaction conditions for the catalytic glycolysis such as the amount of catalyst, solvent, reaction time, and crystallization time have been studied. Furthermore, the recyclability of catalysts has also been investigated. The obtained products after catalytic depolymerization have been identified and characterized using melting point apparatus, thin layer chromatography, 1H-NMR, 13C-NMR and mass spectroscopy. The catalytic performance of LDHs combinations as Zn ˃ Mn ˃ Li, Pb > Cd > Mg > Ni > Co > Ca > Cu has been observed in case of PET while, only ZnAl-CO3 LDH showed catalytic activity in degradation of PC. The catalysts are reusable more than 4 cycles in both case of depolymerization processes without any significant decrease in the activity. The yield of BHET and BPA were observed 79.34 % and 89.07 %, respectively. This work mainly highlighted a sustainable way to design efficient, stable, eco- friendly and recyclable catalysts for PET and PC waste glycolysis into value added products.